Download chemical foundations, 020916

Biology Review
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Chemical Foundations
Note
Much of the text material is from, “Essential Biology with
Physiology” by Neil A. Campbell, Jane B. Reece, and Eric J.
Simon (2004 and 2008). I don’t claim authorship. Other
sources are noted when they are used.
2
Outline
•
Some basic principles
• Organic and biochemistry
3
Some Basic Principles
C
Cu
Fe
Zn
O
N
Mg
H
Mo
P
Cr
S
K
I
Si
Se
Mn
B
Cl
F
Co
Na
Ca
Sn
V
4
Chemical Elements
•
Chemical elements are the fundamental basis of all matter since they
cannot be broken-down into smaller unique elements.
•
92 naturally occurring chemical elements have been identified along
with other elements formed in laboratories.
•
An element is designated by a one- or two-letter symbol; for example,
hydrogen (H), oxygen (O), carbon (C), and sodium (Na).
•
The symbols are typically derived from the Greek, Latin, or English
names.
•
All chemical elements are organized in the periodic table of elements.
5
http://www.cwu.edu
Periodic Table of Elements
6
Life Essential Elements
•
25 of the 92 naturally occurring chemical elements are essential
to life.
–
–
–
Oxygen, carbon, hydrogen, and nitrogen make-up about 96
percent of the mass of the human body.
Much of the remaining 4 percent consists of 7 elements.
Less than 0.01 percent of the human body are trace elements
essential to life.
7
Chemical Composition of the Human Body
Elements
Oxygen (O)—65.0%
Carbon (C)—18.5%
Hydrogen (H)—9.5%
Nitrogen (N)—3.3%
Calcium (Ca)—1.5%
Phosphorous (P)—1.0%
Potassium (K)—0.4%
Sulfur (S)—0.3%
Sodium (Na)—0.2%
Chlorine (Cl)—0.2%
Magnesium (Mg)—0.1%
Trace elements—0.01%
Percentages are listed by weight.
Trace Elements
Boron (B)
Chromium (Cr)
Cobalt (Co)
Copper (Cu)
Fluorine (F)
Iodine (I)
Iron (Fe)
Manganese (Mn)
Molybdenum (Mo)
Selenium (Se)
Silicon (Si)
Tin (Sn)
Vanadium (V)
Zinc (Zn)
8
Teeth and Plaque
•
Teeth are part of the living, dynamic system that makes-up the oral
cavity (mouth).
•
Bacteria reside in plaque, which consists of food, saliva, and dead
cells.
•
Bacteria release acids—especially when a person eats sugars and
refined carbohydrates—that remove minerals from tooth surfaces.
•
Cavities, pain, and tooth loss can occur.
9
Fluoride
Fluoride (F-), an ionic form of the element fluorine, is found in the
earth’s crust.
•
Fluoride dissolves in water when water percolates through ground
and into the aquifer.
•
The crust and groundwater in some areas of North America is missing this trace element.
http://www.toonaripost.com
•
10
Fluoride (continued)
•
Fluoride can help maintain healthy teeth If in sufficient concentration
in drinking water.
•
According to the U.S. Centers for Disease Control (CDC), water
fluoridation reduces tooth decay by about 25 percent over a person's
lifetime.
•
Fluoride helps to re-mineralize tooth surfaces to prevent cavities from
forming.
•
Fluoride can be added to drinking water as part of the treatment process.
11
Chemical Compounds
•
Elements can be combined to form chemical compounds of two or
more elements in fixed ratios.
•
Compounds are far more common than pure elements—examples
include:
–
Water or H2O
– Sodium chloride or NaCl (table salt)
– Glucose and fructose isomers or C6H12O6 (cane and beet sugar)
– Methane or CH4
12
Chemical Compounds (continued)
•
Most compounds in living organisms are made-up of several elements.
•
For example, the nucleotides of DNA and RNA consist of carbon, nitrogen, oxygen, and phosphorous.
Nucleotide
http://biochemicalminds.files.wordpress.com
13
Atoms
•
An element is an atom that is distinctly different from the atoms of
other elements.
•
“Atom” is from the Greek word for indivisible—it is the smallest unit
of matter that retains the unique properties of an element.
•
For example, a carbon atom is the smallest amount of the element,
carbon.
•
Carbon plays key roles in life, as we will discuss.
•
Atoms are very small—for example, about one million carbon atoms
would stretch across a period in a textbook.
14
Structure of Atoms
•
Atoms are composed of subatomic particles called protons, electrons,
and neutrons.
–
A proton has a single unit of positive charge (+).
– An electron has a single unit of negative charge (-).
– A neutron is electrically neutral—it has no electrical charge.
•
The nucleus of an atom has only protons and neutrons, while electrons
are in the surrounding electron cloud.
15
Structure of Atoms (continued)
•
An atom with equal number of protons and electrons is electrically
neutral.
•
For example, a helium atom (He) has two protons, two neutrons,
and two electrons.
•
Electrons surround the nucleus in a pattern described as a cloud
or probability density function.
16
Electron Shells
The inner shells are shown in
blue and outer shells in red.
(Schematic drawing to the
left)
Electron cloud
http://academic.brooklyn.cuny.edu
To provide scale: if the electron cloud
were 100 meters in diameter, the
nucleus would be the size of a housefly.
(Drawing to the right)
http://members.tripod.com/craigjm
17
Atomic and Mass Numbers
•
The number of protons in an atom—its atomic number—determines
the element.
•
For example, the atomic number of oxygen is 8 since it has 8 protons.
•
The mass number is the total number of protons and neutrons in a
nucleus.
•
Oxygen has a mass number of 16, and carbon has a mass number of
12.
18
Mass
•
Mass is a measure of the amount of matter in an object determined
by its atoms.
•
Protons and neutrons have nearly identical masses, while electrons
have about 1/2000 of the individual masses.
•
Even smaller subatomic particles exist, which are known as quarks.
•
Quarks are not particularly relevant to our discussion of chemical elements.
19
Isotopes
•
Isotopes of an element have the same number of protons and electrons
but different numbers of neutrons—therefore, their mass numbers vary.
Attribute
Isotope
Carbon-12
Carbon-13
Carbon-14
Number of protons
6
6
6
Number of neutrons
6
7
8
Atomic number
6
6
6
Mass number
12
13
14
Percentage of all carbon
~ 99%
~ 1%
<< 1%
Stable?
Yes
No
No
•
Carbon-14 (14C) is a naturally-occurring, unstable isotope—its nucleus
decays and emits particles and energy.
•
The degree of instability of 14C is measured by its half-life (5,730 years).
20
http://earthsci.org
Half-Life of Carbon-14
21
Radioactive Isotopes
•
A radioactive isotope emits particles and energy when its nucleus
decays.
•
They have many uses in biological research and medicine since
living cells do not distinguish among isotopes of the same element.
•
Organisms take-up and use radioactive isotopes in their usual biological ways.
•
With uptake by cells, the location and concentration is measured by
the radiation they emit.
22
Radioactive Isotopes (continued)
Radioisotopes are used as tracers to monitor the uptake and use
of atoms and chemical compounds in living organisms.
•
With imaging instruments, such as PET scanners, radioisotopes
are used to monitor chemical processes in the body for research
and medical diagnosis.
http://www.examiner.com
•
23
Can you think of other isotopes used in the health sciences?
24
Electron Arrangement
•
Electrons determine how an atom will behave when it encounters one
or more other atoms.
•
One or more electron shells exist—electrons in the outer shell have
the highest energy levels.
•
The inner shell can accommodate two electrons, while the second and
third shells can each have eight electrons.
25
Electron Shells (again)
The inner shells are shown in
blue and outer shells in red.
(Schematic drawing to the
left)
Electron cloud
http://academic.brooklyn.cuny.edu
http://members.tripod.com/craigjm
26
Electron Arrangement (continued)
•
The number of electrons in the outer shell determines the chemical
properties of an atom.
•
Atoms with outer shells that are not completely full can interact with
atoms whose outer shells are also not full.
27
Comparisons of Some Elements
Element
Atomic number
(number of
protons)
Electrons in
inner shell
(maximum = 2)
Electrons in
outer shell
(maximum = 8)
Additional
electrons that
can be added
Reactive?
Hydrogen (H)
1
1
--
1
Yes
Helium (He)
2
2
--
0
No
Carbon (C)
6
2
4
4
Yes
Nitrogen (N)
7
2
5
3
Yes
Oxygen (O)
8
2
6
2
Yes
Hydrogen, carbon, nitrogen, and oxygen are biologically
important elements, in part, because they can covalently bond
with other atoms.
28
Covalent Bonds
•
Two atoms that share one or more pairs of outer shell electrons form
a covalent bond.
•
The number of covalent bonds that can form is equal to the number
of additional electrons needed to fill the outer shell.
•
For example, the single covalent bond in an H2 molecule (gaseous
hydrogen) completes the single shell of electrons for both hydrogen
atoms.
29
Covalent Bonds (continued)
•
In H2O, two hydrogen atoms share their electrons with an oxygen
atom.
•
In CH4 (methane), four hydrogen atoms share electrons with a carbon atom.
•
In O2 (gaseous oxygen), two atoms share two pairs of electrons to
form a double covalent bond.
30
Ionic Bonds
•
NaCl, composed of sodium and chloride (an ionic form of chlorine), is
formed through an ionic bond.
Element
Atomic
number
Electrons in
inner shell
(maximum = 2)
Electrons in
second shell
(maximum = 8)
Electrons in
third shell
(maximum = 8)
Ionic bond
Sodium (Na)
11
2
8
1
Na donates an
electron to CL and
becomes Na+
Chloride (Cl)
17
2
8
7
Cl accepts an
electron from Na,
and becomes Cl-
•
Before the electron transfer, sodium and chloride are electrically neutral;
after the electron transfer, the atoms are ions—that is, they are electrically
charged.
•
Ions are held together by an ionic bond, the attraction between ions with
opposite charges.
31
Molecular Representations
Several methods can be used to represent molecules of
one or more atoms.
Method
Depiction
Used in this course?
Conventional naming
Text
Yes
Molecular formula
Text
Yes
Electron configuration
Graphic
No
Structural formula
Text or 2-D graphic
Yes
Space-filling model
3-D model
Sometimes
Ball-and-stick model
3-D model
Sometimes
32
Ball-and-Stick Models
DNA
http://upload.wikimedia.org
N-butane
C4H10 or
CH3-CH2-CH2-CH3
http://www.orc.uni-linz.ac
33
Chemical Reactions
•
The chemistry of life is dynamic—chemical reactions in cells rearrange
molecules by breaking chemical bonds and forming new bonds for metabolic and other cellular functions.
•
For example, oxygen and hydrogen gases can react to form water and
produce energy.
2H2 + O2 = 2H2O + energy
H2 and O2 are the reactants and H2O is the product.
•
Matter is neither created nor destroyed—the same number of hydrogen
and oxygen atoms are found in the reactants and products, although they
are arranged differently.
34
Water and Life
•
Life originated in the seas about 3.7 billion years ago, and evolved in
water for about 3 billion years before arriving on land.
•
Life remains tied to water; terrestrial (land) species developed water
retention and regulation mechanisms suited to their physical environments.
•
Cells, surrounded by a fluid consisting mostly of water, have 70 to 90
percent water content.
•
The abundance of water is a key reason life can exist and flourish on
Earth.
35
Hydrogen Bonds
•
A water molecule consists of two hydrogen atoms joined to an oxygen
atom by two covalent bonds.
•
H2O is a polar molecule due to two features:
–
Oxygen, because of its greater mass, attracts the electrons in the
covalent bonds more strongly than hydrogen.
– The V-shape of the molecule (slightly less than 145 degrees).
•
The polarity results in weak attraction, known as hydrogen bonding,
between the hydrogen and oxygen atoms in adjacent water molecules.
36
Hydrogen Bonds (continued)
•
A hydrogen bond is short-lived—it persists for only a few trillionths of a
second.
•
Although only 15 percent of H2O molecules are bonded to four adjacent
H2O molecules at any one time, water is more cohesive than most other
liquids due to hydrogen bonding.
Cohesion = intermolecular force that holds together the molecules
in a solid or liquid.
37
Can you name and describe three types of molecular bonds?
38
Solution, Solvent, and Solute
•
A solution is a liquid that contains one or more substances (such as
sugar).
•
A substance that is dissolved is the solute and the dissolving agent
is the solvent.
•
Water is the solvent in an aqueous solution.
•
Water can dissolve many substances necessary for the sustainment
of life.
39
Water, The Solvent of Life
•
H2O can dissolve ionic salts by orienting its charged regions toward
the oppositely charged regions of these molecules.
•
In sodium chloride (NaCl), Na+ ions attract electrically negative oxygen atoms, and Cl- ions attract positively charged hydrogen atoms in
water molecules.
•
Polar attractions facilitate the dissolving of many types of salt crystals
in water.
•
Other polar molecules, such as sugars, also dissolve readily in water.
40
Acids and Bases
•
Water molecules can dissociate (break apart) into hydrogen (H+) and
hydroxide (OH-) ions.
•
A base—or alkali—is a compound that accepts H+ ions and removes
them from the solution.
•
A chemical compound that donates H+ ions to a solution is known as
an acid.
•
Hydrochloric acid (HCl) in the lumen of the stomach is a strong acid
formed from H+ and Cl- secreted by specialized cells in the stomach
wall.
41
pH Scale
•
The pH (potential hydrogen) scale ranges from 0 to 14—from very
acidic to very basic.
•
Biological fluids have buffers that resist changes in pH to maintain the
organism’s homeostasis (internal equilibrium) for proper functioning of
chemical processes.
Buffer = resists changes in pH by accepting H+ ions when
they are in excess, and donate H+ ions when they are
depleted.
42
Basic
Solution
H+
<
OH-
Increasingly basic
pH Scale (continued)
14
13 Oven cleaner
Household bleach
Household ammonia
11
Milk of magnesia
12
10
9
8
Neutral
Solution
H+ > OHAcidic
Solution
Increasingly acidic
H+ = OH-
7
6
The pH scale is logarithmic. Each
whole unit represents a 10-fold
change in hydrogen
concentration.
Lemon juice (pH 2) has 10 times
more H+ ions than an equivalent
amount of grapefruit juice (pH 3).
Seawater
Pure water
Urine
Human blood
5
4
3
2
Tomato juice
Grapefruit juice
Lemon juice, gastric juice
1
0
43
Organic and Biochemistry
http://library.thinkquest.org
44
All Life is Carbon-Based
Lichen (combination of fungus and
a symbiotic photosynthetic partner)
http://media.wiley.com
http://3611farm1.static.flickr.com
http://www.richardseaman.com
http://www.fs.fed.us
http://www.rspb.org.uk
45
Organic Chemistry
Cells contain mostly water—the remainder is primarily carbon-based
molecules.
•
Carbon can form large, complex, and diverse molecular structures.
•
The study of carbon based compounds is known as organic chemistry.
http://organicglassware.com
•
46
Characteristics of Carbon
•
The versatility of carbon in organic molecules is due to four physical
features:
–
–
–
–
Has four electrons in an outer shell that can hold eight electrons.
Can complete its outer shell by forming covalent bonds with many
other elements including hydrogen, oxygen, and nitrogen.
Serves as an molecular intersection that can branch in four directions.
Is able to bond to other carbon atoms to form intricate and vast
molecular structures.
47
Carbon Backbones
Carbon backbones, or skeletons, can vary in length from very short
to very long, and are:
–
–
–
Unbranched or branched
Organized single or double covalent bonds
Arranged in single-ring or multi-ring structures
Carbon backbone
of a protein
molecule
http://www.scielo.com
•
48
Hydrocarbons
•
The simplest organic compounds are the hydrocarbons, which consist
of carbon and hydrogen atoms.
•
The simplest hydrocarbon is methane (CH4), a carbon atom with covalent bonds to four hydrogen atoms.
•
Methane is:
One of the most abundant hydrocarbons in natural gas.
– Produced by prokaryotic (bacterial) cells in the digestive tracts of
grazing animals (ruminants).
– Produced by prokaryotic cells in swamps, especially in the southeastern states.
–
49
Hydrocarbons (continued)
•
Octane—with its eight carbon molecules—is found in the fossil fuels
(gasoline and diesel oil) used in internal combustion engines.
•
The energy rich components of fat molecules have also have extensive hydrocarbon structures.
http://www.pedrosgarage.com
50
Organic Molecule Shapes
•
Each organic molecule has a unique three-dimensional shape, which is
mostly due to carbon’s ability to form four bonds.
•
Large organic molecules can have elaborate shapes such as branched
and multi-ring structures.
51
Molecular Comparisons
Organic molecules range from
simple to very complex
structures.
A protein molecule
http://nai.nasa.gov
Methane molecule
(CH4)
http://fixedreference.com
52
Are there other atoms that could take the place of carbon
as the basis for life?
53
Functional Groups
•
The properties of an organic compound depend on carbon and other
atoms attached to the carbon skeleton.
•
Atoms that participate in chemical reactions are known as functional
groups.
54
Functional Groups (continued)
•
Four functional groups important in the chemistry of life consist of:
Hydroxyl group (O-H), found in alcohols and sugars
– Carbonyl group (C=O), found in sugars
– Amino group (H-N-H), found in amino acids
– Carboxyl group (O=C-O-H), found in amino acids, fatty acids, and
some vitamins
–
•
Many biological molecules—including amino acids and nucleic acids—
have two or more functional groups.
55
Macromolecules
•
Biological molecules that are very large on a molecular scale are
called macromolecules.
•
Macromolecules include:
Polysaccharides (complex sugars)
– Triglycerides (a type of fat molecule)
– Polypeptide chains and proteins
– Nucleic acids (DNA and RNA)
–
•
The polymer structures of some macromolecules are synthesized
from repeating units of smaller molecules known as monomers.
•
A polymer is like a beaded necklace consisting of many individual
beads.
56
http://k43.pbase.com
String of Pearls
The string is somewhat analogous to identical monomers (simple
sugars) bonded together to form starch, or different monomers
(amino acids) bonded together to form polypeptides.
57
Polymer Formation
•
Polymers are formed from monomers through the process of dehydration synthesis.
•
For each monomer added to a polymer chain, a water (H2O) molecule
is formed by the release of one oxygen and two hydrogen molecules.
•
The monomers replace lost covalent bonds by forming covalent bonds
to each other.
58
Dehydration Synthesis
(H2O)
http://chsweb.lr.k12.nj.us
Monomers are joined through the process of dehydration
synthesis.
59
Breakdown of Polymers
•
Organisms breakdown certain molecules into smaller molecules or
atoms.
•
Starches and proteins in foods consist of chains of long polymers.
•
The polymers must be broken-down (digested) for absorption by the
small intestine to make the monomers available for cell metabolism.
Cell metabolism = the chemical processes occurring within a
living cell or organism that are necessary for the maintenance of
life. In metabolism, some substances are broken down to yield
energy for vital processes while other substances, necessary for
life, are synthesized.
(http://www.thefreedictionary.com)
60
Breakdown of Polymers (continued)
•
The process of hydrolysis reverses the process of dehydration synthesis.
•
The covalent bonds between monomers are broken by adding H2O
along with an enzyme to facilitate the reaction.
61
Hydrolysis
Maltose
+ Enzyme (maltase)
Glucose
Glucose
http://northonline.sccd.ctc.edu
The covalent bonds between the two glucose molecules
are broken-down through hydrolysis.
62
http://www.blackgoldpotatoes.com
Carbohydrates
http://www.dormgear.com
Carbohydrates range from single- and double-sugar molecules
in soft drinks and candy, to the long-chained starch
molecules in pasta and potatoes.
63
Monosaccharides
•
Simple sugars, or monosaccharides, include:
Glucose in sports drinks and corn syrup
– Fructose in fruit
– Fructose and glucose in high fructose corn syrup (HFCS)
–
•
Glucose and fructose are isomers having the same molecular formula
(C6H12O6).
•
These two isomers differ only in the position of a double covalent bond
for an oxygen atom.
•
Many monosaccharides form ring-like structures in aqueous solutions.
64
http://www.biology.clc.uc.edu
Glucose
Molecular formula: C6H1206
The double bond for an oxygen atom is at the first carbon
position. For the fructose, an isomer of glucose, the oxygen
double bond is at the second carbon position.
65
Monosaccharides (continued)
•
Glucose is a primary source of chemical energy for performing cellular
work.
•
It is the only energy source used by the brain and other nervous system tissues.
•
Fructose is converted to glucose by the liver so that it can be used as
an energy source by cells.
66
Disaccharides
•
A disaccharide is a double sugar formed from two monosaccharides
through dehydration synthesis.
•
Disaccharides include:
Sucrose = glucose + fructose (sugar cane, beet sugar)
– Lactose = glucose + galactose (dairy products)
– Maltose = glucose + glucose (beer, malted milk shakes, milk balls)
–
67
Commonly Consumed Sugars
Sugar Components
Sources
Fructose
(percent)
Glucose
(percent)
Comments
Sucrose
50
50
Used in many calorically-sweetened beverage and
food products outside of the U.S. and Canada.
High fructose corn syrup
(HFCS-55)
55
42
Derived from corn syrup. Used in soft drinks and
some juices as a caloric sweetener.
Also derived from corn syrup. Used in baked
goods, jams, and yogurt, including as a caloric
sweetener, browning agent, and shelf life
extender.
High fructose corn syrup
(HFCS-42)
42
53
Fruit
100
0
The caloric density is generally much less than
other sugar sources listed in this table.
Honey
50
50
Nectar contains sucrose, which the honeybee
hydrolyzes into the monosaccharides, glucose and
fructose.
68
Polysaccharides
•
The simplest polysaccharides are long chains of single types of sugar
molecules (recall the pearls on a necklace).
•
Starch—from roots and other plant organs—has many glucose monomers strung together.
•
Plant cells store starch as a source of chemical energy and materials
for synthesizing other molecules.
69
Polysaccharides (continued)
•
Starch in human diets is in potatoes and grains such as wheat, corn,
and rice.
•
Starches are digested in the digestive tract through the hydrolysis of
chemical bonds between glucose molecules.
70
Cellulose
•
Cellulose is the most abundant organic compound—it forms cable-like
fibers in the cell walls that enclose plant cells.
•
Glucose monomers in cellulose are linked in more complex structures
than in starches.
•
Cellulose cannot be digested by most animals (although ruminants are
an exception), and it passes through the digestive tract as fiber (roughage).
•
Fiber—an important dietary component—is found in fruits, vegetables,
whole grains, bran, and beans.
71
http://www.lsbu.ac.uk
Molecular Structure
Cellulose is a complex array of glucose molecules.
Ruminants, such as cows, and wood-eating termites have
bacteria in their digestive systems that break the covalent
bonds in cellulose to enable it to be digested.
72
How many different carbohydrates do you consume
in your diet?
73
Lipids
Lipids are a broad set of biological molecules that include fats, cholesterol, and steroids.
•
All are hydrophobic—that is, they do not mix well with water because
of their chemical properties.
•
In oil and vinegar salad dressing, the oil (a lipid) will separate from the
vinegar consisting mostly of water.
http://www.tivolihome.com
•
74
Fats
•
Triglycerides (type of dietary fat) have a glycerol molecule covalently
bonded to three chains of fatty acid molecules through dehydration
synthesis.
•
Fatty acids are long hydrocarbon chains that store a substantial amount
of energy—a pound of fat contains over twice the potential energy of a
pound of starch.
•
Adipose cells swell and shrink with the deposit and withdrawal of fatty
acids.
75
Fats (continued)
•
Due to its energy efficiency, fat is difficult to burn-off for losing weight.
•
A reasonable amount of body fat is normal and healthy, and serves as
a reserve for chemical energy.
76
Saturated and Unsaturated Fatty Acids
•
A fatty acid is saturated when it has only single bonds and the maximum number of hydrogen atoms.
•
A fatty acid is unsaturated when it has a double bond and less than
the maximum number of hydrogen atoms.
•
An unsaturated fatty acid bends at a double covalent bond in its carbon backbone.
Saturated
Unsaturated
http://telstar.ote.cmu.edu
77
Nutritional Fats
•
A saturated fat has no double bonds in any of its three fatty acid
chains.
•
An unsaturated fat has a double bond in one of its three fatty acid
chains.
•
A polyunsaturated fat has double bonds in two or three of its three
fatty acid chains.
78
Unhealthy Effects
•
Many animal fats—including lard and butter—are high in saturated
fats.
•
The linear shape of the hydrocarbon chains in saturated fatty acids
allow them to stack easily, making saturated fats solid at room temperature.
•
Diets rich in saturated fats can contribute to cardiovascular disease
in a condition known as atherosclerosis.
•
Lipid containing deposits (known as plaque) build-up in the walls of
arteries, reducing blood flow and increasing the risk of heart attacks
and strokes.
http://www.multivu.com
79
At the grocery store, could you pick-out the saturated
and unsaturated fats?
80
Steroids
•
Steroids are lipids since they are hydrophobic—however, they differ
from fats in their molecular structure and functions.
•
The carbon skeleton of a steroid has four rings (labeled A, B, C, and
D).
81
Molecular Structure
C
A
D
B
http://www.abc.net.au
Cholesterol, shown above, is a precursor to other steroids.
They all share similar A-B-C-D ring structures.
82
Cholesterol
•
Cholesterol—a sterol—is a steroid precursor for testosterone, estrogens, and corticosteroids, among others.
•
We will discuss steroids in more detail when will cover endocrinology
and sexual reproduction.
•
Cholesterol is needed by the body to synthesize cell membranes and
to synthesize other molecules.
•
High levels of cholesterol (in particular, LDL) are associated with cardiovascular disease.
83
Anabolic Steroids
•
Anabolic steroids are synthetic (human-made) variants of testosterone,
the male sex hormone.
•
In males at puberty, testosterone stimulates increased muscle and bone
mass, promotes facial and body hair growth, and promotes other masculine traits.
•
Anabolic steroids mimic these effects due to a similar molecular structure.
•
Some professional and amateur athletes use anabolic steroids to enhance
their performance because the margin between winning and losing can be
razor thin.
http://californiaaddictionnetwork.com
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Medical and Societal Concerns
•
The health effects of anabolic steroids include violent mood swings,
depression, liver damage, high cholesterol levels, reduced sex drive,
and infertility.
•
The use of anabolic steroids raises issues of unfair competitive advantage.
•
Theirr use also raises questions about athletes serving as role models
for younger children and adolescents.
85
Mitigation
•
Major League Baseball, professional cycling, and professional wrestling
have been the focus of recent controversies involving anabolic steroids.
•
Many athletic organizations no longer are oblivious to the use of anabolic steroids, and test for anabolic steroids, blood doping, and banned
drugs.
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Proteins
•
Proteins are formed from one or more polypeptide chains that are
synthesized from monomers known as amino acids.
•
The human body contains tens of thousands of different proteins—
each has a unique molecular shape.
•
Protein functions include:
–
–
–
–
–
–
–
Structural
Storage
Contractile
Enzymes
Signal
Transport
Defensive
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Levels of Protein Structure
Primary = amino acid sequence
Secondary = alpha helix or pleated sheet
Tertiary = polypeptide three-dimensional shape
Quaternary = protein three-dimensional shape
A protein consists of one or more polypeptide
chains.
http://upload.wikimedia.org
88
Amino Acids
•
Proteins in our bodies are synthesized from a common set of 20 amino
acids.
•
Each amino acid has a carbon atom covalently bonded to four partners.
Carboxyl group (—COOH)
– Amino group (—NH2)
– Hydrogen atom (—H)
– Side group unique to each amino acid
–
•
The side group gives an amino acid its particular properties.
•
The peptide (covalent) bonds that join amino acids are formed through
dehydration synthesis.
89
Amino Acid Structure
H
Amino
Group
(NH2)
C
Side
Group
Carboxyl
Group
(CH2O)
or
Side
Group
Side
Group
Side
Group
A schematic of a carbon atom and its four covalent partners
in an amino acid.
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Side Groups
Acidic or
Amide
(n = 4)
Aromatic
(3)
Basic
(3)
Aliphatic
(5)
Hydroxyl or
sulfur-containing
(4)
Cyclic
(1)
http://www.bact.wisc.edu
91
Nucleic Acids
•
The names of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
are derived from their origins in the cell nucleus.
•
Nucleic acids consist of long chains of four monomers known as nucleotides.
•
The genes in DNA contain the instructions for synthesizing amino acid
sequences to form polypeptides and proteins.
•
The transcription and translation processes involving DNA and RNA will
be discussed later in the biology review.
92
Nucleic Acids (continued)
•
Each nucleotide has three components: 1) sugar, 2) phosphate group,
and 3) nitrogenous base.
•
The five-carbon sugar is ribose in RNA and deoxyribose in DNA (hence
their names).
•
The nitrogenous base gives a nucleotide its uniqueness.
93
DNA Nucleotide Structure
Nitrogenous bases:
Thymine (T) and cytosine (C)
have single-ring structures
(known as pyrimidines).
CH2
Phosphate
group
Adenine (A) and guanine (G)
have double-ring structures
(known as purines).
Sugar
(deoxyribose)
Deoxyribose + phosphate group = sugar-phosphate backbone
DNA base pairing rules: A with T, and G with C in a double helix
arrangement
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DNA Double Helix
Nitrogenous bases pair-off in the two strands of DNA to form a double
helix structure.
http://www.csulb.edu
•
Two modeling techniques are shown.
95
Can you name and provide a brief description of the
molecules of life?
96